<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>let 命令-禁止变量提升</title>
<script>
//使用 var 声明变量
console.log(x); // undefined
 var x = 10;
 //使用 let 声明变量
 console.log(y); // Cannot access 'y' before initialization
 let y = 20;
 </script>
 </head>
 <body></body>
 </html>